The invention relates to a squeegee assembly for a screen printing machine with a printing table. The squeegee assembly has at least one squeegee, a squeegee holder and at least one carriage that is displaceable across the printing table. The squeegee is held on the carriage by the squeegee holder and can be pressed against the printing table by pressure cylinders. The invention further relates to a screen printing machine with a squeegee assembly according to the invention.
The European Patent EP 0 315 817 B1 discloses a screen printing machine with a printing table and a squeegee that is displaceable across the printing table. A squeegee holder holds the squeegee on a carriage running in guide rails by guides. It is adjustable relative to the printing table in both distance and angle and can be pressed against the printing table. Both ends of the carriage are held directly in the guide rails, and the pressure cylinders are designed as double acting pressure cylinders. A printing angle of the squeegee may be adjusted by pivoting guides at the junction between the squeegee holder and the pressure cylinders. On a side of the carriage opposite the pressure cylinders for the printing squeegee, a flood squeegee may be provided, which can be pressed against the printing table by additional pressure cylinders. The pressure cylinders are each attached to an outer side of the carriage and are longitudinally displaceable in guide rails.
An object of the invention is to provide a compact and reliable squeegee assembly for a screen printing machine.
According to the invention this object is attained by a squeegee assembly for a silk screen printing machine with a printing table, wherein the squeegee assembly has at least one squeegee, a squeegee holder and at least one carriage that is displaceable across the printing table. The squeegee is held on the carriage by the squeegee holder and can be pressed against the printing table by pressure cylinders. The carriage has a U-shaped profile, and at least the cylinder sections of the pressure cylinders are accommodated within the U-shaped profile.
With these measures, at least a part of the pressure cylinders is disposed within the U-shaped profile of the carriage and thereby protected from mechanical damage and dirt. Furthermore, a highly compact design of the carriage is achieved. At the same time, because of the U-shaped cross section of the carriage, the carriage is extremely stable and may be made as an extrusion profile, for example. The very stiff carriage contributes to the high printing precision because the squeegee pressure can be adjusted very precisely.
Electrical and/or pneumatic lines are advantageously run within the U-shaped profile, so that the supply or control lines are also protected from damage and dirt.
An actuator for pivoting the squeegee and/or limiting the stroke of the squeegee may advantageously be arranged within the U-shaped profile section, so that, in the ideal case, the carriage is given a smooth-surfaced exterior, and substantially the entirety of the control and adjustment mechanisms is disposed and protected within the U-shaped profile.
The carriage has advantageously at least one cover plate that covers an open side of the U-shaped profile, such that only the piston rods of the pressure cylinders extend through the cover plate. The cover plate can at the same time be advantageously used as a mounting plate for the pressure cylinders, so that the pressure cylinders can be mounted and adjusted on the cover plate where they are easily accessible, and the cover plate together with the pressure cylinders is then inserted into the U-shaped profile of the carriage. The cover plate in conjunction with the U-shaped profile of the carriage results in an extremely stable configuration of the carriage, which is protected from damage and dirt and is at the same time easy to mount.
The two ends of the at least one carriage are advantageously pivotable relative to the printing table by a respective pivoting assembly.
By this pivoting assembly, different basic positions of the squeegee are approached, for example, a squeegee draining position, a squeegee replacement position and a printing position. Starting from the printing position, the carriage is pivoted, for example, by an approximately 90° angle into a squeegee draining position in which the squeegee is pivoted out of the screen area and over a drainage channel. In a squeegee replacement position, the carriage is pivoted, for example by 160°, so that the squeegee holder is easily accessible from the top to replace the squeegee. Advantageously, at least one of the pivoting assemblies has a first pivoting cylinder for pivoting the at least one carriage about a first angle, for example an angle of between 60° and 120°, to reach a squeegee draining position, and a second pivoting cylinder for pivoting the carriage about a second angle that is different from the first, for example an angle of between 120° and 200°, to reach a squeegee replacement position. By providing separate pivoting cylinders it is possible to keep the control complexity to approach the two different angular positions low and also to realize large pivoting angles without any difficulties.
Advantageously, a printing squeegee carriage and, in parallel thereto, a flood squeegee carriage are provided in the screen printing machine according to the invention. This makes it possible to accommodate and protect the adjustment units also for the flood squeegee within the U-shaped profile of the flood squeegee carriage, for example, pressure cylinders. The two ends of both the flood squeegee carriage and the printing squeegee carriage are advantageously arranged together on a pivoting assembly so as to be pivotable relative to the printing table. The flood squeegee carriage and the printing squeegee carriage are thus pivoted together by means of the pivoting assemblies. Irrespective thereof, each carriage can have a separate actuator to adjust the squeegee angle.
The at least one carriage is adjustable relative to the printing table to adjust a squeegee angle. Thus the adjustment of the squeegee angle for a printing process is done by pivoting the entire carriage. This facilitates the adjustment of the squeegee angle, because the carriage can on the one hand be pivoted using servomotors and on the other hand also from the sides of the printing table. In particular, the operator does not need to bend far across the printing table to reach the adjustment mechanism of the printing squeegee if the printing table is very wide. For the adjustment of the squeegee angle, both ends of the carriage are advantageously held in a slotted link in a holding fixture. A slotted link makes it possible to realize a very large pivoting radius and consequently a very exact squeegee angle adjustment for a printing process. An actuator to adjust the carriage advantageously has a servomotor, a spindle gear and a bevel gear accommodated in the U-shaped profile of the carriage. A drive shaft driven by the servomotor advantageously extends through the slotted link in the holding fixture and is connected to the bevel gear. A spindle of the spindle gear is then connected on the one hand to the holding fixture and on the other hand to the bevel gear and extends, for example, into a spindle bore of a bevel wheel of the bevel gear. This makes it possible to realize a very compact and at the same precisely positionable actuator for the squeegee angle adjustment. Providing the spindle drive makes it possible, for example, to apply even large holding forces during the printing process. Because both ends of the carriage must be adjusted synchronously, a synchronization shaft extending along the carriage between end faces of the carriage is advantageously provided. The synchronization shaft is also advantageously arranged within the U-shaped profile of the carriage.
The squeegee is advantageously held on the carriage by means of a clamping device. The clamping device is actuated by the pressure cylinders. This makes it possible to use the pressure cylinders on the one hand to press the printing squeegee against the printing table or against the printing screen and on the other hand to release or clamp the squeegee at the same time. Advantageously, the clamping device can be actuated in an extreme position of the pressure cylinder, such that a clamping lever of the clamping device strikes a limit stop on the carriage in the extreme position. The squeegee is pressed against the printing screen in an adjustment range that does not include the extreme position of the pressure cylinders. When the pressure cylinder is then moved into the extreme position, for example, into the fully retracted position, a clamping lever of the clamping device strikes a limit stop on the carriage and thereby releases the clamping device. The clamping lever is advantageously configured as a double-armed toggle lever and, in the end position of the pressure cylinders or their piston rods when they are retracted into the carriage, is pushed into a release position by the limit stop provided on the carriage. Providing a toggle lever makes it possible to realize very large clamping forces.
Advantageously, the carriages provided are a printing squeegee carriage and, in parallel thereto, a flood squeegee carriage. Adjustable limit stops are provided in the flood squeegee carriage to limit the stroke of the flood squeegee relative to the printing table. Advantageously, the one or more limit stops in the central area of the printing table can be adjusted independently from the limit stops in the edge area of the printing table. This enables a so-called cambering, which corresponds to a downward deformation of the squeegee in the center of the printing table to compensate any sagging of the screen fabric in large printing screens. The limit stops are advantageously adjustable by means of a stroke limiting device, which is arranged within the U-shaped profile of the flood squeegee carriage and has a servomotor and an opposite limit stop that can be displaced in a slotted link. Using an opposite limit stop displaceable in a slotted link makes it possible to achieve a highly precise adjustment of the opposite limit stop and, moreover, also to apply very large counterforces.
When the squeegee is lifted or pressed down during the printing process, for example, only sufficient pressure to lift the squeegee is applied to the pressure cylinders. This pressure can be approximately 2 bar, for example. On the other hand, to overcome a spring force of the toggle lever for opening, it is necessary to overcome the bias of the spring. To release the clamping device of the printing squeegee, the pressure in the pressure cylinders is then increased to 6 bar, for example.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings for example.